This game has a dull plot of vampire killing and worse purification than the prequel, Boktai 2. At least the graphics are really superb; I was surprised the Nintendo DS could support anime cutscenes, which even had voices. This was the first game I played on the Nintendo DS to have animated cutscenes. The character art is good too but the music didn't impress me much. The story is pretty mediocre. Basically, Aaron and Lucian are on a quest to destroy vampires and the dialogue isn't compelling but I've seen worse.
The gameplay is tolerable except for the boss fights but the shoot ‘em up parts are terrible. You basically have to use the touch screen gimmick for everything. You drag your spaceship and tap enemies; this means that you cannot move while shooting. This makes any generic bullet shooter look like a master plan in comparison to this poor setup that is used for purification.
At least there are some new features. They implemented a dash although it costs you energy. Lunar Knights lacks the solar sensor that was with Boktai 2 meaning that you do not need to depend on your weather conditions in order to use your solar-operated weapons. I doubt this is necessary since the 3 bosses I faced telegraphed their attacks, removing any possible challenge. Basically you just block the small attacks with your shield and run away from the big ones and you can win with just the normal weapons.
Aaron and Lucian play slightly different, with Aaron requiring energy for his Solar Gun and Lucian using a sword. However, Aaron's Solar Gun requires energy, which makes dashing indoors worthless because it costs you energy and you can only recharge at certain points, excluding recovery items. Both characters use elementals called terrenials too. The dashing problem is made worse because the areas feel bigger than the predecessor, which encourages you to dash; it shouldn't have a cost or it should have its own meter rather than the energy meter if they wanted me to use it temporarily.
Both Aaron and Lucian can do a trance, which makes boss fights even more of a joke. This lets them drain energy or life and bite rapidly for high damage. At least it quickens those awful battles. The main difficulty is with that bullet shooter part which makes you have to change the habit of shooting and moving to shoot once or twice and then dodge, which is a chore as well as prolong those boss battles; imagine if any bullet shooter was like that. It would be flat-out terrible; they could have you use the touch screen to drag the ship and press L or R to shoot. I'd rather do the purifications from Boktai 2 because at least those were original and done properly although you just had to push them into the area where the satellite beams intersected. At least you can block though. What doesn't make any sense is the fact they let your guard regenerate with its own meter when you're not using it but not your dashing, which shares the energy meter.